Material and method for three-dimensional modeling

ABSTRACT

A three-dimensional model and its support structure are built by fused deposition modeling techniques, wherein a thermoplastic material containing silicone is used to form the support structure and/or the model. The thermoplastic material containing silicone exhibits good thermal stability, and resists build-up in the nozzle of an extrusion head or jetting head of a three-dimensional modeling apparatus. The silicone contained in a support material acts as a release agent to facilitate removal of the support structure from the model after its completion.

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application is a continuation-in-part of U.S. applicationSer. No. 09/854,220, filed May 11, 2001, which is hereby incorporated byreference as if set forth fully herein.

BACKGROUND OF THE INVENTION

[0002] This invention relates to the fabrication of three-dimensionalobjects using additive process modeling techniques. More particularly,the invention relates to forming three-dimensional objects by depositinga first solidifiable material in a predetermined pattern so as to form athree-dimensional object, in coordination with the depositing of asecond solidifiable material so as to provide a support structure forthe three-dimensional object as it is being built.

[0003] Additive process modeling machines make three-dimensional modelsby building up a modeling medium, based upon design data provided from acomputer aided design (CAD) system. Three-dimensional models are usedfor functions including aesthetic judgments, proofing the mathematicalCAD model, forming hard tooling, studying interference and spaceallocation, and testing functionality. One technique is to depositsolidifiable modeling material in a predetermined pattern, according todesign data provided from a CAD system, with the build-up of multiplelayers forming the model.

[0004] Examples of apparatus and methods for making three-dimensionalmodels by depositing layers of solidifiable modeling material from anextrusion head are described in Valavaara U.S. Pat. No. 4,749,347; CrumpU.S. Pat. No. 5,121,329; Batchelder, et al. U.S. Pat. No. 5,303,141;Crump U.S. Pat. No. 5,340,433; Batchelder, et al. U.S. Pat. No.5,402,351; Crump, et al. U.S. Pat. No. 5,503,785; Batchelder, et al.U.S. Pat. No. 5,764,521; Danforth, et al. U.S. Pat. No. 5,900,207;Batchelder, et al. U.S. Pat. No. 5,968,561; Stuffle, et al. U.S. Pat.No. 6,067,480; and Batchelder et al. U.S. Pat. No. 6,238,613; all ofwhich are assigned to Stratasys, Inc., the assignee of the presentinvention. The modeling material may be supplied to the extrusion headin solid form, for example in the form of a flexible filament wound on asupply reel or in the form of a solid rod, as disclosed in U.S. Pat. No.5,121,329. As described in U.S. Pat. No. 4,749,347, modeling materialmay alternatively be pumped in liquid form from a reservoir. In anycase, the extrusion head extrudes molten modeling material from a nozzleonto a base. The extruded material is deposited layer-by-layer in areasdefined from the CAD model. A solidifiable material which adheres to theprevious layer with an adequate bond upon solidification is used as themodeling material. Thermoplastic materials have been found particularlysuitable for these deposition modeling techniques.

[0005] Another layered-deposition technique for building models from asolidifiable material deposits droplets of modeling material fromnozzles of a jetting head. Examples of apparatus and methods for makingthree-dimensional models by depositing layers of solidifiable modelingmaterial from a jetting head are described, for example, in U.S. Pat.No. 5,136,515 to Helinski et al., and U.S. Pat. No. 6,193,923 to Leydenet al.

[0006] In creating three-dimensional objects by additive processtechniques, such as by depositing layers of solidifiable material, it isthe rule rather than the exception that supporting layers or structuresmust be used underneath overhanging portions or in cavities of objectsunder construction, which are not directly supported by the modelingmaterial itself. For example, if the object is a model of the interiorof a subterranean cave and the cave prototype is constructed from thefloor towards the ceiling, then a stalactite will require a temporarysupport until the ceiling is completed. Support layers or structure maybe required for other reasons as well, such as allowing the model to beremoved from a base, resisting a tendency for the model to deform whilepartially completed, and resisting forces applied to a partiallycompleted model by the construction process.

[0007] A support structure may be built utilizing the same depositiontechniques and apparatus by which the modeling material is deposited.The apparatus, under appropriate software control, produces additionalgeometry acting as a support structure for the overhanging or free-spacesegments of the object being formed. Support material is depositedeither from a separate dispensing head within the modeling apparatus, orby the same dispensing head that deposits modeling material. The supportmaterial is chosen so that it adheres to the modeling material.Anchoring the model to such support structures solves the problem ofbuilding the model, but creates the additional problem of removing thesupport structure from the finished model without causing damage to themodel.

[0008] The problem of removing the support structure has been addressedby forming a weak, breakable bond between the model and the supportstructure, such as is described in U.S. Pat. No. 5,503,785. The '785patent discloses a process by which a material that forms a weak,breakable bond with the modeling material is selected as either asupport material or a release coating. Support material is deposited inlayered fashion at the interface between the object and its supportstructure, or it is deposited in a layered fashion to form the supportstructure, in either case permitting the support structure to be brokenaway after formation of the object. When a release coating is used, itis deposited at the interface between the object and its supportstructure as a liquid, and forms a layer so thin that its geometry maybe disregarded in the construction of the object.

[0009] In filament-fed Stratasys FDM® three-dimensional modelingmachines of the current art, a filament strand of the modeling material(or support material) is advanced by a pair of motor-driven feed rollersinto a liquifier carried by the extrusion head. Inside the liquifier,the filament is heated to a flowable temperature. The liquifier ispressurized by the “pumping” of the strand of filament into theliquifier by the feed rollers. The strand of filament itself acts as apiston, creating a pump. As the feed rollers continue to advancefilament into the extrusion head, the force of the incoming filamentstrand extrudes the flowable material out from the dispensing nozzlewhere it is deposited onto a substrate removably mounted to a buildplatform. Stratasys FDM® three-dimensional modeling machines of thecurrent art use as the modeling material anacrylonitrile-butadienestyrene (ABS) thermoplastic composition or a waxmaterial. High-impact polystyrene has been used to create a break-awaysupport structure. Additionally, Stratasys offers a material disclosedin pending U.S. patent application Ser. No. 10/019,160, sold under thename Waterworks™, for creating a soluble support structure.

[0010] An apparatus and method for layered deposition of high-strengthengineering polymers to manufacture durable three-dimensional objects isdisclosed in U.S. Pat. No. 6,067,480. Feed rods of the polymer areextruded from an extrusion cylinder using a piston which is displacedinto the cylinder, providing high pressure extrusion accommodating ofpolymers having low melt flow and long chain lengths. The '480 patentdiscloses that feed rods of polycarbonate, polyaryletherketone andpoly(methylmethacrylate) were successfully extruded using the extrusioncylinder apparatus. The '480 patent makes no disclosure of supportmaterials.

[0011] Apparatus and methods for building three-dimensional models bylayered deposition of high-temperature engineering thermoplastics aredisclosed in pending U.S. patent application Ser. Nos. 09/804,401 and10/018,673. These applications disclose the use of polycarbonates,polyetherimides, polyphenylsulfones, polysulfones, polyethersulfones andamorphous polyamides for building a three-dimensional model, butdisclose no materials formulated for use in building a break-awaysupport structure for such a model.

[0012] There is a continuing need to improve model strength and quality,by building models from high-performance engineering thermoplastics.Materials compatible with the modeling process are needed that willprovide a suitable support structure for models built fromhigh-performance materials.

BRIEF SUMMARY OF THE INVENTION

[0013] The present invention is a thermoplastic material containingsilicone, and a method for using the material to build athree-dimensional model by layered deposition modeling. A methodaccording to the present invention employs the thermoplastic materialcontaining silicone as a support material for building a supportstructure for the model while it is under construction, with thesilicone acting as a release agent to facilitate removal of the supportstructure from the model after its completion. The silicone releaseagent also exhibits good thermal stability, facilitating use of thematerial in high-temperature build environments. Advantageously, thesilicone further serves to prevent a build-up of material in the nozzleof an extrusion head or jetting head of a three-dimensional modelingapparatus. Thus, the thermoplastic material of the present invention isused to advantage as a modeling material for building the model itself,in addition to its use as a support material.

[0014] For use as a support material, the thermoplastic material of thepresent invention preferably contains between about 1 and 10 weightpercent silicone. For use as a modeling material, the thermoplasticmaterial of the present invention contains a lesser amount of silicone,preferably between about 0.5 and 2 weight percent silicone. A basepolymer of the thermoplastic material is selected based upon variousphysical, thermal and rheological properties demanded by the depositionmodeling process.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a diagrammatic illustration of a model and a supportstructure therefor formed using layered extrusion techniques.

DETAILED DESCRIPTION

[0016] The present invention is described with reference to a depositionmodeling system of the type shown in FIG. 1. FIG. 1 shows an extrusionapparatus 10 building a model 26 supported by a support structure 28according to the present invention. The extrusion apparatus 10 includesan extrusion head 12, a material-receiving base 14 and a material supply18. The extrusion head 12 moves in X and Y directions with respect tothe base 14, which moves in a vertical Z direction. The material supply18 supplies a feedstock of material to the extrusion head 12. In thedescribed embodiment, a solid feedstock of material is supplied to theextrusion head 12, and is melted in a liquifier 22 carried by theextrusion head 12. The liquifier 22 heats the feedstock material to atemperature slightly above its solidification point, reducing it to amolten state. Molten material is extruded through an orifice 24 of theliquifier 22 onto the base 14. The feedstock may take the form of acontinuous filament, rods, slugs, pellets, granulations or the like.

[0017] The movement of the extrusion head is controlled so as to depositmaterial onto the base 14 in multiple passes and layers to build thethree-dimensional model 26 and further to build the support structure 28defined so as to physically support the model 26 as it is being built.The model 26 and its support structure 28 are build up on the base 14within a build chamber (not shown) having an environment controlled soas to promote thermal solidification. A first layer of the depositedmaterial adheres to the base 14 so as to form a foundation, whilesubsequent layers of material adhere to one another.

[0018] A modeling material A is dispensed to form the model 26, and asupport material B is dispensed in coordination with the dispensing ofmodeling material A to form the support structure 28. For convenience,the extrusion apparatus 10 is shown with only one material supply 18. Itshould be understood, however, that in the practice of the presentinvention, the modeling material A and the support material B areprovided to the extrusion apparatus 10 as separate feedstocks ofmaterial from separate material supplies. The extrusion apparatus 10 maythen accommodate the dispensing of two different materials by: (1)providing two extrusion heads 12, one supplied with modeling material Aand one supplied with support material B (such as is disclosed in theBatchelder '561 patent); (2) providing a single extrusion head suppliedwith both the modeling material A and the support material B, with asingle nozzle for dispensing both materials (such as is shown in FIG. 6of the Crump '329 patent); or (3) providing a single extrusion headsupplied with both materials, with each material dispensed through aseparate nozzle (such as shown in FIG. 6 of the Crump '785 patent).

[0019] In the described embodiment, the modeling material A and thesupport material B are deposited as substantially continuous “roads” inhorizontal layers from an extrusion head, and are supplied to theextrusion head in solid form. It will be understood by those skilled inthe art that the invention can be practiced with advantage in variousother types of modeling machines as well, including those that employ ajetting head, and that the materials may alternatively be supplied tothe extrusion head in liquid form.

[0020] Rheology of Modeling and Support Materials:

[0021] The modeling material A and support material B must satisfy alarge number of modeling criteria for the particular modeling system inwhich they are used, relating generally to thermal properties, strength,viscosity and adhesion.

[0022] The modeling material A and support material B must have a meltviscosity suitable for the modeling process. Ideally, materials used forfused deposition modeling have low melt viscosity. The melt viscositymust be low enough at the extrusion temperature so that it can beextruded as a generally continuous road or bead. Also, the meltviscosity at the extrusion temperature must be low enough so thatdeposited roads or beads of material have little melt strength, allowingthem to lay flat rather than curl up. Melt viscosity is lowered byincreasing the temperature at which the material is extruded. Too highan extrusion temperature, however, can cause heated material sittingidle in the extruder to decompose. If decomposed, in the case of afilament-pump extruder that has no positive cut-off mechanism, thematerials will drain uncontrollably from the liquifier into the buildenvelope, a condition referred to as “ooze”. Further, a lower extrusiontemperature reduces energy consumption, reduces heat generation andreduces the opportunity to degrade polymeric material.

[0023] In theory, the viscosity of a melt is related to the molecularweight of the material, and as it approaches the critical molecularweight, properties diminish. So, the lower limit on melt viscosity isdefined as that at the critical molecular weight, but virtually allcommercial grade polymers exceed the critical molecular weight todeliver good physical properties.

[0024] Melt viscosity may be measured by its inverse parameter, meltflow. A material used to build models in a Stratasys FDM® modelingmachine which has a filament-pump extruder must have a high melt flow atthe extrusion temperature, so as to be extruded as a continuous beadunder a relatively low pressure of about 3000 psi or less. A desirablehigh melt flow for material deposited by a filament-pump type extruderis greater than about 5 gms/10 minutes, as measured by ASTM D1238, undera load of 1.2 kg at the extrusion temperature. Most preferably, the meltflow is between 5-30 g/10 minutes. A lower melt flow (higher viscosity)is suitable for high pressure extrusion, such as by the apparatusdisclosed in U.S. Pat. No. 6,067,480.

[0025] To properly support the model under construction, the supportmaterial B must bond to itself (self-laminate). The support materials Bmust form a weak, breakable bond to modeling material A (co-laminate),so that it can be separated from the completed model without causingdamage to the model. Where the support structure is built up from thebase, support material B must additionally bond to the base.

[0026] To produce a dimensionally accurate model, the modeling andsupport materials must exhibit little shrinkage upon cooling in theconditions of the build envelope. Any shrinkage of the support materialB must match that of the modeling material A. A shrink differential inthe materials would cause stresses and bond failures along themodel/support structure joint. Amorphous polymers typically have ashrinkage upon solidification of less than or equal to 0.010 inch/inchaccording to ASTM injection-molding test standards. The shrinkagecharacterisitic of amorphous polymers is acceptable for depositionmodeling purposes, while crystalline polymers exhibit shrinkage too highfor deposition modeling. Fillers may be added to the materials to reduceshrinkage. Crystalline additives may be added to the materials of thepresent invention, so long as they are added in an amount small enoughso that the materials continue to exhibit the shrinkage characteristicof an amorphous polymer.

[0027] Selection of a particular modeling material A can be madeaccording to the particular application of the finished model. Thesupport material B must have sufficient mechanical strength in solidform to provide support to a model during its formation. The supportmaterial B must resist forces by the modeling material A, or the modelwill exhibit undesirable curling and deformation. A tensile strength ofbetween 3000 psi and 12,000 psi is typically desired.

[0028] The modeling material A and support material B, when supplied infilament or rod form, must be strong enough to be shipped withoutbreaking. When supplied in filament form, the materials must furtherhave the strength and flexibility to be formed into a filament, bespooled and unspooled, and be fed through the extrusion apparatuswithout breakage. Similarly, materials supplied in filament form musthave sufficient rigidity to not be deformed by compressive forces duringfeeding through the extrusion apparatus.

[0029] As to thermal properties, the modeling material A and supportmaterial B should have similar heat deflection properties, so that bothmaterials can successfully be extruded into the same build chamber. Astaught in U.S. Pat. No. 5,866,058, building the model in a chamberheated to a temperature higher than the solidification temperature ofthe thermoplastic or other thermally solidifiable modeling material,followed by gradual cooling, relieves stresses from the material. Thestresses are annealed out of the model while is being built so that thefinished model is stress free and has very little distortion. As isfurther taught in the '058 patent, a modeling material should have aglass transition temperature (T_(g)) higher than the temperature of thebuild chamber, so that the model does not become so weak that it droops.The preferred temperature of the build chamber is thus in a rangebetween the solidification temperature of modeling material A and itscreep relaxation temperature (creep relaxation temperature is defined asthe point at which the stress relaxation modulus has dropped by a factorof ten from its low temperature limit). Likewise, the glass transitiontemperature of the support material B should be higher than thetemperature of the build chamber, so that the support structure will notdeform and will maintain structural fidelity of the model that itsupports. It has been discovered through experimentation that the glasstransition temperature (or heat deflection temperature) of the supportmaterial B should be within about 20° C. of the of the modeling materialA, preferably with 15° C. The addition of fillers to the materials canhave the effect of raising a material's glass transition temperature. Inpractice, glass transition temperature is indicated by the heatdeflection temperature. Heat deflection temperature of the exemplarymaterials disclosed herein is measured by the DMA softening point of thematerial.

[0030] Exemplary polymers for use as modeling material A or supportmaterial B, or for use in formulating such materials, includepolyethersulfones, polyetherimides, polyphenylsulfones, polyphenylenes,polycarbonates, high-impact polystyrenes, polysulfones, polystyrenes,acrylics, amorphous polyamides, polyesters, nylons, PEEK, PEAK and ABS.The selection of a particular material formulation is made based uponthe various physical, thermal and rheological properties demanded by thedeposition modeling process, such as have been described. A supportmaterial formulation is further chosen based upon the strength of thebond it will have the modeling material. The bond between the supportmaterial and modeling material must be strong enough to secure the modelin place during its formation, but weak enough to permit removal of thesupport structure from the model after construction is complete.

[0031] It should be noted that while materials are referred to herein aseither “modeling” or “support” materials, these materials may beinterchanged so as to form a model using the so-called “support”material and to form a support structure for that model using theso-called “modeling” material. In a given build process, however, thematerial used for forming the model will desirably have properties thatare superior to those of the material used to form its support structure(e.g., greater strength and toughness).

[0032] Testing of Materials:

[0033] The following are examples of material formulations which weretested for use as support materials in a very high-temperature modelingenvironment (i.e. build chamber temperature of 200° C. or greater). Thematerial formulations were tested as support materials for apolyphenylsulfone modeling material. Specifically, in each case, thepolyphenylsulfone modeling material is Radel® R 5600 NT (available fromBP Amoco). This polyphenylsulfone resin has a heat deflectiontemperature of 236° C., and a melt flow in the range of 20-30 gms/10min. at 400° C. under a 1.2 kg load. Example 3 embodies the presentinvention, while Example 1 and 2 are comparative examples.

[0034] All of the materials tested met the rheology criteria discussedabove. In each case, techniques conventional in polymer chemistry wereused to compound the component materials. The exemplary materials weresuccessfully formed into modeling filament of a very small diameter, onthe order of 0.070 inches, and used in a filament-fed depositionmodeling machine. Materials according to the examples given were testedusing filament-fed layered deposition modeling machines of the typedisclosed in pending U.S. application Ser. Nos. 09/804,401 and10/018,673, which are hereby incorporated by reference as if set forthfully herein.

EXAMPLE 1

[0035] Models of various sizes were built in a build chamber having atemperature of about 200-225° C., using the polyphenylsulfone modelingmaterial and a support material comprising a blend of polyphenylsulfoneand amorphous polyamide. In some cases, the support material furtherincluded polysulfone. Weight percent ranges of the various componentmaterials were between about 60 and 90 weight percent polyphenylsulfone,and between about 10 and 40 weight percent amorphous polyamide blend, orbetween about 60 and 90 weight percent polyphenylsulfone, between about1 and 40 weight percent polysulfone and between about 10 and 40 weightpercent amorphous polyamide blend. A particular exemplary resin testedis a blend of 50 weight percent Radel® R 5600 NT polyphenylsulfone(available from BP Amoco), 25 weight percent Udel® P 1710 NT 15polysulfone (available from BP Amoco), and 25 weight percent EMS TR 70amorphous polyamide (available from EMS-Chemie AG of Switzerland). Thisresin has a heat deflection temperature of 224° C. and a melt flowsimilar to that of the modeling material. The support material wasextruded from a liquifier having a temperature of about 350° C. to forma support structure for a model built using the polyphenylsulfone resin.

[0036] The support material according to this example was satisfactoryfor models that took less than about 20 hours to build, but failed formodels that had a longer build time. It was observed that the supportmaterial exhibited thermally instability after about 20 hours in thebuild chamber. The thermally instability manifested by the materialbecoming dark and eventually blackening, and becoming strongly adheredto the model. Desirably, a material will survive build times of up toabout 200 hours, to permit the building of large and complex parts.Thus, while the support material of the present example was foundsatisfactory for supporting small parts, it is not suitable for moregeneral high-temperature use.

EXAMPLE 2

[0037] Test models were built in a build chamber having a temperature ofabout 200-225° C., using the polyphenylsulfone modeling material and asupport material which comprised various resins of polyethersulfone,polyphenylsulfone or polyetherimide (i.e., Ultem™). These materialsexhibited favorable thermal stability, but could not be broken away fromthe model. The support material containing polyphenylsulfone adheredvery strongly to the model. The support material containingpolyetherimide adhered fairy strongly to the model, and the supportmaterial containing polyethersulfone, while exhibiting the leastadherence to the model, adhered too strongly for suitable use.

EXAMPLE 3

[0038] Large and small polyphenylsulfone models were built in a buildchamber having a temperature of about 200-225° C., using a supportmaterial comprising a polyethersulfone base polymer and a siliconerelease agent. For convenience, commercially available compounds wereused to provide a “masterbatch” containing silicone, which wascompounded with the base polymer. Various masterbatches were tested,which included polypropylene, linear low-density polyethylene, andhigh-impact polystyrene. Additionally, various silicones were tested,ranging in viscosity from about 60,000 centistokes (intermediateviscosity) to 50 million centistokes (very high viscosity). The veryhigh viscosity silicones have a high molecular weight, while the lowerviscosity silicones have a lower molecular weight.

[0039] It was found that intermediate viscosity silicone was a muchbetter release agent than the very high viscosity silicone, and that thehigh-impact polystyrene masterbatch released more easily from thepolyphenylsulfone modeling material than did the other masterbatchestested. In a preferred embodiment, the masterbatch contained about 75weight percent of a high-impact polystyrene copolymer and about 25weight percent of a 60,000 centistoke (cSt) viscosity silicone. In thisembodiment, the support material comprised between about 90-95 weightpercent polyethersulfone, between about 3-8 weight percent high-impactpolystyrene, and between about 1-3 weight percent silicone. Thiscomposition was demonstrated using BASF, Ultrason E-1010polyethersulfone and Dow-Corning MB25-504 styrene butadiene copolymercontaining hydroxy-terminated poly dimethyl siloxane (i.e.hydroxy-terminated silicone). This material was extruded from aliquifier having a temperature of about 420° C. to successfully form asupport structure for a model built using the polyphenylsulfone resin.The support structure satisfactorily released from the model after itsconstruction.

[0040] The support material of the present example exhibited a tensilestrength of between 5000 psi and 12,000 psi, exhibited a shrinkagetypical of amorphous polymers (less than 0.010 inch/inch), a melt flowin the range of about 5-30 gms/10 min. under a 1.2 kg load at atemperature of up to 450° C., and a heat deflection temperature of about232° C.

[0041] Discussion of Results

[0042] It was demonstrated that adding a small amount of silicone to abase polymer weakened the bond between the base polymer and the modelingmaterial, enabling use of the polymer to form a support structure thatcould be broken-away from the model. An intermediate viscosity silicone(on the order of about 10⁴-10⁵ centistokes) provided good releasecharacteristics, although it is expected that a variety of silicones canbe used to advantage in the present invention.

[0043] As the silicone release agent exhibited thermal resistance attemperatures of 225° C. for over 200 hours, the present invention isparticularly useful in supporting models made from high-temperaturethermoplastics in a very hot environment. Heretofore, there have been noknown materials suitable for building a support structure by layereddeposition modeling techniques in an environment hotter than about 180°C.

[0044] While the composition of the present invention was demonstratedusing a polyethersulfone base polymer, the silicone release agent can beadded to a variety of other base polymers to likewise lessen adhesion ofthe support structure to the model. A base polymer is selected basedupon various physical, thermal and rheological properties demanded bythe deposition modeling process. For high-temperature processes,silicone added to a polyphenylsulfone or polyetherimide base polymerwill exhibit good thermal stability. Other potential base polymers foruse in various build environments include polyphenylenes,polycarbonates, high-impact polystyrenes, polysulfones, polystyrenes,acrylics, amorphous polyamides, polyesters, nylons, PEEK, PEAK and ABS.Where adhesion between a base polymer and a modeling material is higher,a greater amount of silicone can be added. A suitable amount of siliconewill weaken but not destroy the bond between the support structure andthe model, providing adhesion sufficient to support the model underconstruction. It is expected that up to about 10 weight percent siliconemay be desired in some cases.

[0045] While a high-impact polystyrene co-polymer was used indemonstrating the present invention, such co-polymer is but one exampleof a copolymer which may be included in the composition of the presentinvention. The high-impact polystyrene masterbatch was used as a matterof convenience in compounding the silicone with the base polymer. Thoseskilled in the art will recognize that various masterbatches may be used(e.g., one made with the base polymer of the support material), thatother techniques for compounding may be used which do not require amasterbatch (e.g., liquid silicone could be added directly to the basepolymer), and that various other co-polymers may be included in thethermoplastic composition, in various amounts, to satisfy processingdemands of a given application.

[0046] An unexpected benefit of the thermoplastic material containingsilicone is that this material resisted build-up in the nozzle of theextrusion head liquifier. This attribute of the material, thoughunintended, is highly desirable. Typically, the liquifier of anextrusion-based layered deposition modeling machine needs to be replacedafter extrusion of only about 7 pounds of material, due to anunacceptable build up of material in the nozzle. Resistance to cloggingof the material containing silicone was observed to surpass that of anymaterials heretofore known in the art. The nozzles of liquifiers used toextrude the thermoplastic material containing silicone extruded over 40pounds of the material before needing replacement. Nozzle life was thusextended by over 400 percent. Hence, silicone was demonstrated toprovide the thermoplastic with characteristics desirable for modelingmaterials as well as support materials.

[0047] Resistance to nozzle clogging was demonstrated with compositionsthat included as little as 0.75 weight percent silicone. For modelingmaterials, the amount of silicone in the material may thus be kept verysmall, between about 0.5 weight percent and 2 weight percent, to prolongthe liquifier life without degrading the strength of the modelingmaterial. As will be recognized by those skilled in the art, the higherviscosity silicone, which has a lesser release ability, may bebeneficial as an additive to the modeling material. As will be furtherrecognized by those skilled in the art, where silicone is contained inboth the modeling and support material, a reduced amount of silicone inthe support material may be preferred.

[0048] Also as will be recognized by those skilled in the art, themodeling material A and support material B may include inert and/oractive filler materials. The fillers can provide enhanced materialproperties which may be desirable depending upon the intended use of theresulting model. For instance, fillers can provide RF shielding,conductivity, or radio opaque properties (useful for some medicalapplications). Fillers can alternatively degrade material properties,but this may be acceptable for some uses. For instance, an inexpensivefiller can be added to the modeling material A or support material B todecrease the cost of these materials. Fillers can also change thermalcharacteristics of the materials, for instance a filler can increase theheat resistance of a material, and a filler can reduce materialshrinkage upon thermal solidification. Exemplary fillers include glassfibers, carbon fibers, carbon black, glass microspheres, calciumcarbonate, mica, talc, silica, alumina, silicon carbide, wollastonite,graphite, metals and salts.

[0049] Filler materials which will assist in removal of the supportstructure can also be used in the composition of the present invention.For instance, a filler material that swells when contacted by water oranother solvent will tend to be useful in breaking down the supportstructure. A filler material that evolves gas when contacted by water oranother solvent will likewise tend to be useful in breaking down thesupport structure.

[0050] Those skilled in the art will recognize that innumerable otheradditives may also be to modify material properties as desired forparticular applications. For instance, the addition of a plasticizerwill lower the heat resistance and melt flow of a thermoplasticmaterial. The addition of dyes or pigments can be done to change color.An antioxidant can be added to slow down heat degradation of material inthe extruder.

[0051] The modeling and support materials A and B of this foregoingexamples may be molded into filament, rods, pellets or other shapes foruse as a modeling feedstock, or it may be used as a liquid feedstockwithout prior solidification. Alternatively, the mixture may besolidified and then granulated.

[0052] It is noted that the modeling material A and support material Bof the foregoing examples are moisture sensitive. It has beendemonstrated that exposure of these materials to a humid environmentwill significantly degrade model quality, thus, maintaining dryconditions is important. In order for the materials of the presentinvention to build accurate, robust models by fused depositiontechniques, the material must dried. Particularly suitable apparatus forbuilding up three-dimensional objects using the high temperature,moisture-sensitive materials of the present invention are disclosed inpending U.S. application Ser. Nos. 09/804,401 and 10/018,673, which areincorporated by reference herein. The '673 application discloses amodeling machine having a high-temperature build chamber, and the '401application discloses a moisture-sealed filament cassette and filamentpath for supplying moisture-sensitive modeling filament in afilament-fed deposition modeling machine.

[0053] For the modeling material A and support material B of theforegoing examples, an acceptable moisture content (i.e. a level atwhich model quality will not be impaired) is a level less than 700 partsper million (ppm) water content (as measured using the Karl Fischermethod). The '401 application discloses techniques for drying thefilament provided in the a filament cassette. One method for drying thematerial is to place a cassette containing the material in an oven undervacuum conditions at a suitable temperature (between 175-220° F. istypical) until the desired dryness is reached, at which time thecassette is sealed. The cassette may then be vacuum-sealed in amoisture-impermeable package, until its installation in a machine. Anexpected drying time is between 4-8 hours to reach less than 300 ppmwater content. Another method is to dry the material by placing packetsof desiccant in the cassette without use of the oven. It has beendemonstrated that placing packets containing Tri-Sorb-molecular sieveand calcium oxide (CaO) desiccant formulations in the cassette andsealing the cassette in a moisture-impermeable package will dry thematerial to a water content level of less than 700 ppm, and will dry thematerial to the preferred range of 100-400 ppm. This desiccant-onlydrying method has advantages over the oven-drying method in it requiresno special equipment, and is faster, cheaper and safer than oven drying.Suitable Tri-Sorb-molecular sieve desiccant formulations include thefollowing: zeolite, NaA; zeolite, KA; zeolite, CaA; zeolite, NaX; andmagnesium aluminosilicate.

[0054] The '401 application further discloses a filament delivery systemand an active drying system which will preserve the dryness of thematerial when it is loaded in the modeling machine. The drying systemcreates an active moisture barrier along a filament path from thecassette to the extrusion head, and purges humid air from the modelingmachine. The drying system continuously feeds dry air or other gas underpressure to the filament path, disallowing humid air from remaining inor entering the filament path, and is vented at or near the end of thefilament path.

[0055] Although the present invention has been described with referenceto preferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

1. An additive-process method for building a three-dimensional modelcomprising the step of: depositing layers of a thermoplastic compositioncontaining between about 0.5 and 10 weight percent silicone.
 2. Themethod of claim 1, wherein the thermoplastic composition contains lessthan about 2 weight percent silicone and the thermoplastic compositionforms the model.
 3. The method of claim 1, wherein the thermoplasticcomposition contains greater than about 1 weight percent silicone andthe thermoplastic composition forms a support structure for the model.4. The method of claim 1, wherein the thermoplastic composition furthercomprises a base polymer selected from the group consisting ofpolyethersulfones, polyetherimides, polyphenylsulfones, polyphenylenes,polycarbonates, high-impact polystyrenes, polysulfones, polystyrenes,acrylics, amorphous polyamides, polyesters, nylons, PEEK, PEAK and ABS.5. The method of claim 1, wherein the thermoplastic composition has aheat deflection temperature of greater than about 220° C.
 6. The methodof claim 5, wherein the thermoplastic composition has a melt flow in therange of about 5-30 gms/10 min. under a 1.2 kg load at a temperature ofup to 450° C., and a tensile strength of between about 5,000 psi and12,000 psi.
 7. The method of claim 6, wherein the base polymer isselected from the group consisting of polyethersulfones,polyphenylsulfones and polyetherimides.
 8. The method of claim 1,wherein the silicone has a viscosity on the order of about 10⁴-10⁵centistokes.
 9. The method of claim 1, wherein the silicone ishydroxy-terminated polysiloxane.
 10. The method of claim 1, wherein thethermoplastic composition has a heat deflection temperature of greaterthan about 40° C., a melt flow in the range of about 5-30 gms/10 min.under a 1.2 kg load at a temperature of up to 450° C., and a tensilestrength of between about 3,000 psi and 12,000 psi.
 11. The method ofclaim 1, wherein the thermoplastic composition is deposited into a buildchamber having a temperature of between about 180° C. and 250° C.
 12. Anadditive-process method for building a three-dimensional model and asupport structure therefor, the model being formed by layered depositionof a solidifiable modeling material and the support structure beingformed by layered deposition of a solidifiable support material, whereinthe support material is a thermoplastic composition comprising betweenabout 1-10 weight percent of a silicone release agent.
 13. The method ofclaim 12, wherein the support material further comprises a base polymerselected from the group consisting of polyethersulfones,polyetherimides, polyphenylsulfones, polyphenylenes, polycarbonates,high-impact polystyrenes, polysulfones, polystyrenes, acrylics,amorphous polyamides, polyesters, nylons, PEEK, PEAK and ABS.
 14. Themethod of claim 12, wherein the support material has a heat deflectiontemperature of greater than about 220° C.
 15. The method of claim 14,wherein the support material has a melt flow in the range of about 5-30gms/10 min. under a 1.2 kg load at a temperature of up to 450° C., and atensile strength of between about 5,000 psi and 12,000 psi.
 16. Themethod of claim 15, wherein the base polymer is selected from the groupconsisting of polyethersulfones, polyphenylsulfones and polyetherimides.17. The method of claim 16, wherein the base polymer is polyethersulfoneand wherein the support material further comprises high-impactpolystyrene.
 18. The method of claims 16 or 17, wherein the modelingmaterial comprises as a major component of a polyphenylsulfone resin.19. The method of claim 12, wherein the silicone release agent has aviscosity on the order of about 10⁴-10⁵ centistokes.
 20. The method ofclaim 12, wherein the silicone release agent is hydroxy-terminatedpolysiloxane.
 21. The method of claim 12, wherein the support materialhas a heat deflection temperature of greater than about 40° C., a meltflow in the range of about 5-30 gms/10 min. under a 1.2 kg load at atemperature of up to 450° C., and a tensile strength of between about3,000 psi and 12,000 psi.
 22. The method of claim 12, wherein thesupport material is deposited into a build chamber having a temperatureof between about 180° C. and 250° C.
 23. A thermoplastic composition foruse in layered-deposition three-dimensional modeling, comprising a basepolymer selected from the group consisting of polyethersulfones,polyetherimides, polyphenylsulfones, polyphenylenes, polycarbonates,high-impact polystyrenes, polysulfones, polystyrenes, acrylics,amorphous polyamides, polyesters, nylons, PEEK, PEAK and ABS, andbetween about 0.5-10 weight percent silicone, and having a heatdeflection temperature of greater than about 40° C., a melt flow in therange of about 5-30 gms/10 min. under a 1.2 kg load at a temperature ofup to 450° C., and a tensile strength of between about 3,000 psi and12,000 psi.
 24. The thermoplastic composition of claim 23, wherein thebase polymer is selected from the group consisting of polyethersulfones,polyphenylsulfones and polyetherimides, and wherein the heat deflectiontemperature is greater than about 220° C.
 25. The thermoplasticcomposition of claim 24, wherein the composition exhibits thermallystability for a time period of at least 200 hours at temperatures of upto about 225° C.
 26. The thermoplastic composition of claim 23, whereinthe silicone is hydroxy-terminated polysiloxane.
 27. The thermoplasticcomposition of claim 23, wherein the weight percent of the base polymerin the composition ranges from about 60 percent to about 99 percent. 28.The thermoplastic composition of claim 27, wherein the thermoplasticcomposition further comprises between about 3-15 weight percenthigh-impact polystyrene.
 29. The thermoplastic composition of claim 28,wherein the base polymer is polyethersulfone.
 30. The thermoplasticcomposition of claim 29, wherein the weight percent of polyethersulfonein the composition ranges from about 90-95 percent, the weight percentof high-impact polystyrene in the composition ranges from about 3-8, andthe weight percent of the silicone release agent in the compositionranges from about 1-3 percent.
 31. The thermoplastic composition ofclaim 23, in the form of an extrudable object.
 32. The thermoplasticcomposition of claim 31, wherein the extrudable object is a filament.33. The thermoplastic composition of claim 23, and further comprising upto 20 weight percent of a filler.